Placed on the Web Jan 97 by the NSF Center for IPM
North Carolina Information

KNOW AND CONTROL CUCUMBER PESTS

MANAGEMENT PRACTICES F0R AVOIDING CUCUMBER PR0BLEMS

Diseases, pests, and disorders remain a threat to efficient cucumber production and good profits by lowering yields, reducing quality, and making harvests unreliable. The risk of these problems can be reduced by wise management.

Poor stands may be caused by cold or wet soils, improper seeding depth or fertilization, residual herbicides, insects, and damping-off caused by several soil inhabiting fungi such as Pythium spp., Rhizoctonia spp., Fusarium spp., and some leafspotting fungi during wet periods. CONTROL: Follow general management practices, replant.

Seedcorn maggot, adult, larva, pupa (Delia platura) and injury to seedlings. In the spring adults seek germinating seeds to lay eggs. Maggot injury is associated with cold, wet, organic soils. CONTROL: Apply soil insecticide, replant.

Wireworm larva and adults (Conoderus vespertinus and C. falli) and injury to small plant. Wireworms are associated with fields previously in small grain or not in row crops. CONTROL: Avoid problem fields and use soil insecticide.

Herbicide injury from residues carried over from previous crop, most often corn. Herbicide injury is fairly common as there are many possibilities for misuse. CONTROL: Keep records of herbicides used in fields; select proper herbicide(s), application method and rates; check equipment calibration; avoid drift; clean equipment properly.

Cold injury is very serious on cucumbers. It is most likely to show up in low areas. CONTROL: Follow general management practices, replant.

Fertilizer injury often occurs with banded fertilizer. Symptoms include poor stands, marginal foliar burning, and browning of roots. CONTROL: Adjust equipment properly, broadcast fertilizer according to soil test reports, reapply fertilizers if needed as determined by soil test or soluble salts.

Serpentine leafminer larva, pupa and adults (Liriomyza spp.) and injury. Their presence is common but serious injury is usually confined to small plants. CONTROL: Early detection and prompt insecticide sprays.

Cucumber beetle damage. This insect overwinters as adults and harbors the wilt bacterium. Typically in early spring their feeding causes reduced stands, distorted plants, and wilt, especially on small seedlings. CONTROL: Early detection and prompt insecticide sprays.

Spotted and striped cucumber beetle adults and larva (Diabrotica undecimpunctata howardi and Acalymma vittatum) on plant with bacterial wilt. The beetles are overwintering sources and vectors of the bacterial wilt pathogen. Wilt often involves only a portion of a plant. CONTROL: Follow general management practices, early detection of beetles and prompt insecticide sprays. Frequent sprays are required.

Squash bug adults, eggs, and nymphs (Anasa tristis) and plant damage. Squash bugs are serious pests of squash and may occur on other cucurbits. Adults and nymphs suck plant juices which blackens and dries out vines. CONTROL: Apply insecticide sprays against the immature stages.

Aphid colonies (Aphis gossypii and others) and damage. Winged and wingless aphids occur on the underside of leaves. These sucking insects cause little feeding injury, however they spread viruses that cause mosaic. CONTROL: Apply insecticides if populations are very large. This is not effective for controlling mosaic.

Pickleworm (Diaphania nitidalis) and characteristic entrance hole with exudate. The movement of pickleworm moths into North Carolina and their presence in specific fields are monitored with sex pheromone traps or occurrence on squash plants. CONTROL: Begin spraying when migration is detected.

Pickleworm (Diaphania nitidalis) and relatives:

  1. Early instar pickleworm. Note brown head and black spots.
  2. Late instar pickleworm. Note brown head and green body.
  3. Melonworm (Diaphania hyalinata). Note white stripes on top of body.
  4. Pickleworm. Again note brown head with a black notch on the rear of the head capsule and the green body.
  5. Squash vine borer (Melittia cucurbitae). Note the black head and the white, deep segmented body.
  6. Squash vine borer moth. These moths visit curcurbits during the day.

Fertilizer deficiency. Characteristic symptoms of manganese deficiency. CONTROL: Apply fertilizers according to annual soil test reports.

Soybean thrips (Sericothrips variabilis) and injury. Feeding winged and wingless, yellow or striped, narrow bodied thrips cause silvery blotches on leaves and reduced plant vigor, especially on small plants during cool, wet periods. CONTROL: Scout fields for presence of thrips and spray when infestations occur. Use a lOx pocket magnifier and white paper to detect thrips.

Two spotted spider mite adult and egg (Tetranychus urticae) and foliar injury Mites suck plant juices causing yellowed leaves and poor plant growth. With population buildup during hot, dry periods, fine webbing may be observed. CONTROL: Same as for soybean thrips.

Cabbage looper adult, pupa and larva (Trichoplusia ni) and injury. Foliar feeding by loopers can strip leaves and delay growth of small plants in late plantings. CONTROL: Check traps for this migrating insect, scout fields and spray when young larvae are seen.

Deformed fruit often results from poor pollination, extreme weather (too hot, dry, wet, cold) or nutrition levels (too much or little fertilizer). CONTROL: Place one bee colony per acre after flowering, fertilize according to soil test reports, and irrigate.

Honey bee (Apis mellifera). Honey bees are essential for successful cucumber pollination and production. At least one strong colony per acre is needed to ensure adequate bee activity. Colonies should be placed in the field after the onset of significant flowering.

Gummy Stem Blight is common and is caused by the seed-borne fungus Mycosphaerella citrullina and the soil-borne fungus Phoma exiqua. All cucurbits are susceptible, and depending on the weather, stem and leafspotting may occur on young plants, especially in late plantings. CONTROL: Follow general management practices; start spray schedule at first appearance.

Anthracnose is common and is caused by the seedborne fungus Colletotrichum lagenarium. Most cucurbits are susceptible. Most commercial cucumber varieties have some resistance. Depending on weather, leaf and fruit spotting may occur on young plants, especially in late plantings. CONTROL: Follow general management practices; start spray schedule at first appearance.

Angular Leafspot is infrequent and is caused by the seed-borne bacterium Pseudomonas lachrymans which can also affect squash and pumpkins. Warm, wet weather may cause stem and leaf spots in midseason. CONTROL: Follow general management practices; start spray schedule at first appearance; do not enter fields when plants are wet.

Powdery Mildew is caused by two air-borne fungi Erysiphe cichoracearum and Sphaerotheca fulginea, but is rarely seen since most commercial cucumbers have excellent resistance. Powdery mildew is often serious in dry weather and is the main cause of early dying of cantaloupes, pumpkins, squash, and greenhouse cucumbers. CONTROL: Resistant cultivars; sprays; because of fungicide specificity and possible development of resistance in the fungus, switch fungicides if spraying is not effective.

Scab is caused by the seed-borne fungus Cladosporium cucumerinum which also affects muskmelons. It is rare because most commercial cucumbers have excellent resistance. Cool night temperatures and high humidities are required. In the active phase, dark, olive-green, velvety mold covers the spot. Leaves, fruit, and young terminals may be affected. CONTROL: Use resistant varieties, spray at first appearance.

Downy Mildew is caused by the air-borne fungus Pseudoperonospora cubensis. Although serious on late season cantaloupes, pumpkins, squash, watermelon, and other cucurbits, it is seldom a problem on cucumbers because most commercial varieties have adequate resistance. The fungus overwinters in Florida, and each year the spores are blown northward and arrive in North Carolina from May to August, if at all. Typically its arrival coincides with summer rains. CONTROL: Resistant cultivars; start spray schedule at first appearance.

Target Spot is caused by the air-borne fungus Corynespora cassiicola which attacks many different plants. It is more common on cucumbers in greenhouses than in fields. CONTROL: Follow general management practices; start spray schedule at first appearance.

Scab on fruit. See No. 5 for description and control.

Belly Rot is caused by the fungus Rhizoctonia solani, present in agricultural soils. It causes damping-off of many crops including cucumbers. Belly rot is common, but its occurrence and intensity are unpredictable. CONTROL: Avoid problem fields; apply fungicide to soil prior to fruit set; keep harvested cucumbers cool, well ventilated; use chlorine in wash.

Bacterial Wilt is caused by the bacterium Erwinia tracheiphila. It overwinters in and is spread by cucumber beetles. Often seen in early to mid-season cucumbers and when temperatures are cool, it occurs on muskmelon and to a lesser extent on squash and pumpkin; watermelons may be immune. CONTROL: Control the cucumber beetles, spray.

Root-Knot is caused by Meloidogyne spp. These nematodes are usually present in agricultural fields and affect many crops. They are especially damaging on plants growing in light, sandy soils when counts are high. CONTROL: Promptly disk all crops after harvest, treat soil with a fumigant nematicide when warranted by assay report.

Mosaics are caused by viruses. Depicted is Tomato Ringspot, fairly common in the northwestern part of the state. The virus resides in wild brambles and is transmitted by some nematodes. Most commercial cultivars have excellent resistance to Cucumber and Watermelon Mosaic. Until recently mosaics were rarely seen in the eastern counties. Because Zucchini Yellow Mosaic (closely related to Watermelon Mosaic) may be introduced, it is important to identify all mosaics. Mosaic viruses are transmitted by aphids and related insects. CONTROL: Select resistant cultivars; avoid problem fields; start spray schedule with stylet oil and insecticides at the seedling stage; use aluminum plastic mulch.

Cottony Leak is caused by the fungus Pythium spp. Present in agricultural soils; it causes damping-off of many crops including cucumbers. Cottony leak is common, but its occurrence and intensity are unpredictable. CONTROL: Avoid problem fields; apply fungicide sprays to soil and foliage prior to fruit set; keep harvested cucumbers cool, well ventilated; use chlorine in wash.

TREATMENTS

Selection of Insecticides and Miticides and Minimum Days to Harvest1,2

Insect or Mite1 GuthionO B. thuringiensis7 diazinon2 Kelthane0 Sevin30 Thiodan3 Pydrin1 methoxychlor1 Phosdrin1-3 methomyl3O Dibrom15 parathion3 phosphamidon
Aphids--++--+++-++-+-++
Cucumber beetle+---+++++++++++
Cutworm+---++++++-+++-+
Leafminer--++-------+--
Looper+++--++++-++++++-
Melonworm----+++++-+++-+-
Mite---++------++--
Pickleworm2----+++++-+++-+-
Seedcorn maggot--++----------
Squash bug--++-+++++++++++-
Squash vine borer+----+++-+-++-
Thrips--+-+++++++++++-
Wireworm--++----------
- do not use, not effective, or no information
+ partially effective
++ most effective, or first choice.

1 This information is provided only for background and is based on field observations. The use of trade names does not imply endorsement or criticism of similar products not mentioned. Actual selection and uses of insecticides and acaricides must follow product labels. Tank mixes are probably more effective. As insects may develop resistance to a pesticide with repeated use, alternate insecticides where possible.
2 Apply insecticides in later afternoon to minimize bee kills.
3Repeated use may induce leafminer and mite problems.

Selection of Fungicides and Nematicides and Minimum Days to Harvest1

Disease5 Maneb, Mancozeb0 Bravo0 Benlate0 Difolatan1 Bayleton5 Ridomil MZ0 Copper (fixed)- PCNB0 Sulfur1 Vydate- Furadan- DD- Vorlex- Vapam- Telone C-17- Vorlex 201
Angular leafspot2------++---------
Anthracnose+++++--+---------
Bacterial wilt2,4------++---------
Belly rot-+-+------------
Cottony leak-----++------++++
Damping-off5-----+-+----++++++++
Downy mildew++-+-++3+---------
Gummy stem blight+++++--+---------
Mosaic (aphid)5----------------
Powdery mildew-+++3-+3-+-+-------
Root-Knot (nematode)---------++++++++
Scab+++++--+-+-------
Scab on fruit+++++--+---------
Target spot+++++--+---------
Tom. Ringspot Mosaic-----------++++++++
- do not use, not effective, or no information
+ partially effective
++ most effective, or first choice.

1 This information is provided only for background and is based on field observations. The use of traded names does not imply endorsement or criticism of similar products not mentioned. Actual selection and uses of insecticides andf acaricides must follow product labels. Tank mises are probably more effective. As insects may develope resistance to a pesticide with repeated use, alternate insecticides where possible.
2Tank mixes with maneb or mancozeb are probably more effective
3Fungus may develope resistance to fungicide; if so, switch fungicide
4Use insecticide to control beetles.
5Use PCNB or Rhizoctonia-, and Ridomil for Pythium-damping off.
6Sylet oil, aphicides, aluminum, reflective mulch

USEFUL RES0URCES AND REFERENCES

Disease and Insect Identification

Plant Disease and Insect Clinic
Box 7616
N. C. State University
Raleigh, N. C. 27695-7616

Nematode, Soil and Plant Analyses

Agronomic Division
N. C. Department of Agriculture
Raleigh, N. C. 27611

Professional Advisory and Educational Services.

County Agent
Agricultural Extension Service
County Seat
Office in Every County

Growing Pickling Cucumbers in North Carolina

AG-315, illus., 15pp., 50 cents
N. C. Agricultural Extension Service
NCSU, Raleigh, N. C. 27695-7603

North Carolina Agricultural Chemical Manual

312pp. Revised Annually. $7.50
N. C. Agricultural Extension Service
NCSU, Raleigh, N. C. 27695-7603

Insect and Related Pests of Vegetables

AG 295, illus., 173 pp., $7.00
N.C. Agricultural Extension Service
NCSU, Raleigh, N.C. 27695-7603

Use of trade names does not imply endorsement of the products named or criticism of similar ones not mentioned.

This poster is provided by the North Carolina Pickle Growers Association, Inc. in cooperation with the North Carolina Agricultural Extension Service to assist growers in cropping efficiency. For more information contact your County Agent.

Prepared by:

Charles W. Averre, Extension Plant Pathologist
Kenneth A. Sorensen and Charles J. Eckenrode, Extension Entomologists
George R. Hughes, Extension Horticulturalist
In cooperation with research colleagues at North Carolina State University